Late Transition Metal Complexes in Olefin Oligomerization

Billions tons of polyolefin-based materials are produced annually. Through a simple insertion reaction, inexpensive and abundant olefins are transformed into polymeric materials for a wide range of applications, including plastics, fibers, and elastomers. Despite its long history, the polyolefin industry is continuing to grow steadily and remains technologically driven because of continuous discoveries of new catalysts, processes, and applications. The key technology that continues to drive the polyolefin industry is transition metal catalyzed polymerization/oligomerization. The discovery of the Ziegler–Natta catalysts in the 1950s not only revolutionized polyolefin production, but also set the way to the development of modern organometallic chemistry. The next milestone in olefin polymerization catalysis was the development of metallocene catalysts in the 1980s. Whereas the Ziegler–Natta and metallocene catalysts still remain as the workhorse in the polyolefin industry, the last decade has witnessed a number of major breakthroughs in the development of Cp-free late transition metal catalysts (Cp = Cyclopentadiene) for the efficient olefin polymerization/oligomerization. These new systems show many exciting features, including high catalytic efficiency, excellent control of polyolefin stereoregularity and branching topology, and most excitingly the tolerance towards functional olefins and/or polar monomers. Indeed, the lower oxophilicity together with a greater functional-groups tolerance of late transition metals, relative to early metals, make them targets for the development of catalysts for the co-polymerization/co-oligomerization of ethylene with polar comonomers under mild conditions. Systems based on Pd , Ru , and Rh have been successfully employed for the dimerization of acrylates. Despite the major disadvantage of reduced activity in olefin insertion reactions, late transition metals remarkably marched into sophisticated field of industrially relevant source materials for polymerization catalysis.